What you're looking for is something called "cascading value lists". If you search for that term on the forum, you should find several threads. Here's one to get you started.
There are different methods the cascading value lists Mike describes is a native Filemaker way. I used to use those a lot in the past.
But since the advent of ExecuteSQL I started using that to populate value lists. Very flexible and you can "select" the values from almost everywhere.
It relies on a trick that ain't supposed to work but it does :-)
Once you get the hang of it, a new world opens :-)